WO2008052670A1 - Method for the production of polyurethane block foam - Google Patents

Abstract

The invention relates to a method and a device for the production of polyurethane block foam, wherein the reaction mixture, after flowing through a mixer (1), flows freely out of an outlet opening (15), and then flows into an accumulation chamber (4) in which a static pressure is built up, then flows through a slot (6), and finally flows through an expansion chamber (8).

Description

 Process for producing polyurethane block foam

The invention relates to a method and a device for producing polyurethane block foam, in which the reaction mixture flows freely after flowing through a mixer from an outflow opening and then flows through a stagnation chamber, in which a static pressure is built up, a gap and finally an expansion chamber.

The continuous production of polyurethane block foam today essentially works according to two different methods:

• the so-called liquid laydown driving style as well

• the trough driving style.

Both methods are described e.g. in the plastic manual volume 7 from the Hanser publishing house described. (3rd, revised edition, 1993, ISBN 3-446-16263-1, page 197-200)

The main difference between these two methods is that the liquid reaction mixture is entered in the trough mode of operation from below into a trough from which it emerges partially expanded over an overflow edge on the bottom paper, while liquid in the Laydown-style liquid on the Bottom paper is applied.

A fundamental advantage of the liquid laydown mode of operation is the fact that, in contrast to the trough procedure, possibly existing air bubbles in the reaction mixture, which can lead to voids in the later foam, can escape into the atmosphere after discharge to the bottom paper. This is e.g. In the manufacture of film stock (i.e., when the foam block is later cut into film stock), a very important advantage is that voids can quickly result in large scrap quantities.

The liquid laydown procedure is usually operated today with a rectangular device in which in the early expansion stage of the polyurethane foam (PUR foam) mats are placed with an adjustable force on the rising foam, thereby achieving a rectangular as possible block cross-section , which leads to a small amount of waste. This method is also described in the Kunstoff-Handbuch Volume 7 (3rd, revised edition, 1993, ISBN 3-446-16263-1, page 197-200) and in GB-A-1392859 and GB-A-1487848 and is the literature known as Hennecke Planibloc rectangle method. This method has been improved in the patent DE-A-2557572 in that the cover paper is already placed on the still liquid reaction mixture to avoid trapped air due to a non-uniform climbing profile at the first contact of the foam with the cover paper. In this case, the cover paper, even before the foam begins to rise, so far lowered, that between the bottom paper and cover paper, a gap is formed, which is so small that the reaction mixture easily accumulates before this gap. Another positive side effect of this gap is its distribution effect. The accumulation of reaction mixture favors the distribution of the reaction mixture to the full width. The cover paper is generally made slightly narrower than the foaming width, so that the mixture is in contact with the atmosphere on the sides. By foaming width is meant the width of the polyurethane reaction mixture foaming on the conveyor belt or base paper, which ultimately corresponds to the width of the resulting foam. This width is defined by the distance of the lateral mold walls in the region of the foaming and curing zone.

A disadvantage of this method is the non-optimal age distribution of the reaction mixture when entering the expansion zone. With a non-uniform flow allows this

Although generally the distribution of the mixture to the required width, but the quantity distribution across the width is still very inhomogeneous. It flows in the middle

Reaction mixture at a higher speed and thus with greater amount in the

Expansion zone as in the peripheral areas. As a result, the foaming process starts in the middle only further downstream than in the edge regions. Since the lower conveyor of these facilities in

Production direction is basically inclined downwards (either with a constant angle of eg 4 ° over the entire production length or adjustable via adjustable plates, the so-called fall plates, at first eg 5 - 8 meters), this can lead to the more liquid mixture components with a higher density subvert the lighter mixture components with a lower density and advance further and further. This then causes serious

Faults in the foam and leads to rejects. This danger of anticipatory liquid

Mixtures in the middle thus limits the angle of inclination of the lower conveyor belt.

At the same time, however, there is also the risk that, if the climbing profile is too steep in the expansion zone, material reflux, especially in the peripheral areas, can occur. However, the limited steepness of the climbing profile means that block height and belt speed must be in a certain ratio.

It should be noted that it is of course eager to produce as high as possible blocks, as this reduces the losses in the top layer and the bottom layer in percent. The block height is otherwise limited primarily by the fact that with increasing block height the Density distribution in the block worsens because higher pressure is applied to the lower layers during foaming than on the upper layers. Ultimately, these boundary conditions therefore mean that the machines have to be operated with a certain minimum belt speed of approx. 4 m / min and accordingly also with high discharge rates of up to 500 kg / min due to the process. This also makes sense, as long as the machine is still operated with good utilization. In reality, however, this often means that the plants run only a few hours a day, which then the investment costs compared to the other costs are relatively large, so that a continuous block foam machine only works economically at a relatively large annual production.

An improvement of the method could be achieved with the calibration plate described in EP-A-0689920. As a result of the fact that the reaction mixture now flows through a gap over a relatively long distance, the distribution effect is improved so that the faster flowing mixture is braked more strongly. Nevertheless, there is still the problem that the downward inclination is limited by the risk of underflowing of older mixture by younger mixture and that at the same time at a too low inclination angle and a steep uphill profile, the reaction mixture in the edge areas in the worst Case can flow back against the conveying direction. Therefore, even with this method, relatively narrow limits are set with regard to the achievable foam height as a function of the belt speed.

A method which deals with the production of blocks with steep rise profile (with the aim of achieving the highest possible blocks) is described in DE-A-2726084. In one embodiment of this method (Figure 2), the mixture is conveyed from above via a transverse distributor tube and a baffle into a trough-shaped trough, from which it reaches the bottom foil via a feed plate, reacting according to the description (page 4) before application is left. Further, as shown in Figure 2, there is a visible gap between the baffle 36 and the bottom foil which makes it impossible to create a significant static pressure at that location. If the mixture is still flowable, it would flow backwards through this gap at a significant static pressure and react there, which would greatly hinder the running of the film and would probably lead to a tearing or stoppage of the bottom foil.

The closest prior art to the inventive solution is disclosed in EP-A-25084. The gap formed between the mixture feed table and the transverse distribution element is similar in side view to a superficial view of the accumulation chamber according to the invention. - A -

The device in EP-A-25084, however, is a pure distributor organ, the task of which consists solely in distributing the mixture to the full width up to the beginning of the kink frothing zone. A complete seal against static fluid pressure in the lower part of the gap as well as at the bend is neither mentioned in the text nor recognizable on the illustrations. This is not necessary at all because under the operating conditions for which the method was developed, which are also described in the examples, no static pressure is produced at the outer edges. The total thickness of the later webs was only 40 mm at a density of 30 kg / m ³ , so that a maximum static pressure of 12 Pa can arise from the foaming side. This minimal static backpressure in conjunction with the high belt speed already ensures that no material reflux can take place in the edge region and thus the problem underlying the invention did not exist at all.

Accordingly, the device described in EP-A-25084 does not have an all-round seal in the transition region from the accumulation chamber to the expansion zone. Therefore, no appreciable static form over the entire foaming width can be constructed with this device, so that at steeper climbing profiles and / or larger foaming heights (> 500 mm) material flows back into the edge regions.

The problem underlying the invention of a slow-running continuous block foam machine, however, has already been taken up in the patent EP-A-1328388. However, the proposed solution of a closed system from the dosing unit to the expansion zone brings with it problems:

possible pulsations in the system, e.g. from the dosing unit or from the mixer unit (e.g., by gas pockets which may then be entrained) may, in principle, propagate into the expansion zone since there is no decoupling of the systems due to contact with the ambient atmosphere;

Gas bubbles, which can develop anywhere in the system, can no longer escape and inevitably lead to voids in the later foam;

It is by no means trivial to distribute the mixture evenly over a width of 2 meters in a closed system with a good age distribution, while avoiding the formation of dead zones under various operating conditions (flow rates, viscosities). In DE-A-69112786 page 5 it is noted that in the open trough, "seen across the width of the channel, significant variations in the While this disadvantage in open trough operation can still be compensated by the fact that the mixture at the outlet from the trough along the interface with the atmosphere can flow freely to the side, the speed at which the reacting foam mixture flows from the vessel outlet to the conveyor If this is no longer possible in a closed system, there is actually a greater risk that a preferred channel is formed, through which the main portion of the reaction mixture flows preferentially, which then leads to a very unfavorable age distribution.

The technical object of the present invention is to provide a method and an apparatus for the production of polyurethane slab foam at low belt speeds of 0.5 to 3 m / min while avoiding the disadvantages mentioned above.

For this reason, in the solution according to the invention, the decoupling of the metering, mixing and discharge region, which has been developed for higher delivery rates, is used by the expansion zone. The pressure required to avoid backflow of material with a steeper uphill profile and low belt speeds of 0.5 to 3 m / min is not applied by the metering devices but by the static pressure resulting from the static height.

The invention relates to a continuous process for the preparation of polyurethane block foam in which the reactive components polyol and isocyanate are metered to a mixer (1) and mixed therein to form a polyurethane reaction mixture and the polyurethane reaction mixture applied to a conveyor belt (7) is, foams and hardens on, characterized in that

a) the polyurethane reaction mixture after mixing from the mixer (1) through at least one outflow opening (15) is discharged freely flowing and through the feed opening (3) in a stagnation chamber (4) into it, which extends in the vertical direction and after the Side is closed, and opens in the region of the bottom in a gap opening (5), and

b) the polyurethane reaction mixture in the accumulation chamber (4) is dammed so that static pressure is generated at the bottom of the accumulation chamber over the entire width, and the polyurethane reaction mixture flows through the accumulation chamber (4) from top to bottom, and

c) the polyurethane reaction mixture then flows through the gap opening (5) from the accumulation chamber (4) and flows through a gap (6), the underside of the Gap is formed by a conveyor belt (7) and wherein the gap is closed up and down and at the lateral edges, and

d) the polyurethane reaction mixture subsequently flows from the gap (6) into the expansion chamber (8) and foams therein, wherein the conveyor belt (7) forms the underside of the expansion chamber (8), and wherein the expansion chamber (8) on the side Is closed edges, and wherein the flow cross-section of the expansion chamber in the transport direction of the conveyor belt (7) expands, and

e) the foamed polyurethane reaction mixture exits through an outlet opening from the expansion chamber and optionally further foams and hardens on the conveyor belt (7).

Here, "free-flowing" in step a) means that the PUR reaction mixture is not completed from all sides, but contact with the environment, e.g. to the atmosphere. Thereby, the above-mentioned, to avoid cavities very advantageous Filmentsgasung is possible and the expansion area is decoupled from the metering and mixing unit.

In one possible embodiment of the method according to the invention, the polyurethane mixture after mixing in the mixer initially flows through a hose or a pipeline and optionally also through a pressure adjusting device, such as e.g. a throttle before it is discharged through the outflow freely flowing.

The static pressure which is generated at the bottom of the accumulation chamber is advantageously in a range from 100 to 5000 pascals, preferably from 150 to 3000 pascals and more preferably from

200 to 2000 Pascal. At the bottom of the accumulation chamber then there is an absolute pressure, which the

Sum of the ambient pressure and the static pressure corresponds. The inventive method ensures that builds up a sufficient static form over the entire width of the accumulation chamber, since only by a backflow can be reliably prevented even in the edge regions.

In the context of this invention, the term static static pressure means the pressure which the liquid column in the accumulation chamber would exert in the static state. He follows the formula

p = p - g - h where h is the length measure from the upper liquid level, ie the interface of the reaction mixture to the atmosphere, to the bottom of the accumulation chamber (represented by the gap opening). With an average density of, for example, 1100 kg / m ³ and the gravitational acceleration of 9.81 m / s ^2, a static admission pressure of 540 Pascal would result, for example, with a liquid column of 5 cm. In addition, of course, the drag forces of the paper act on the reaction mixture. In addition, the actual static pressure drops locally depending on the gap size

by the dynamic proportion - v ² , where v is the rate of the reaction mixture

means.

A static pre-pressure of 100 Pascal on the sides is sufficient to compensate for 50 cm rise height at a bulk density of 20 kg / m ³ and thereby reliably avoid relative flow of reaction mixture to the separation web in the opposite direction to the conveying direction.

Therefore, the static pressure at the bottom of the accumulation chamber should also be at least 100 Pascal, also in the edge region, which corresponds to a liquid column of about 1 cm. Since the reaction mixture should leave the vertically inclined accumulation chamber but still substantially liquid, the accumulation chamber must not be too long.

Of course, the accumulation chamber must be extended in the vertical direction, because only then is it possible to generate a static admission pressure with a defined, limited retention time. Accordingly, the accumulation chamber requires in addition to the lateral limiting walls inclined to the horizontal rear wall and inclined to the horizontal front wall.

Preferably, at least one lateral boundary surface of the accumulation chamber, ie at least the front and / or rear boundary surface in the direction of production and / or at least one lateral boundary surface, is clamped by a conveyor belt or a separating web guided thereon, for example a paper web. In this case, the accumulation chamber is preferably extended only so long that the reaction mixture, which is in contact with the separation web drawn through the accumulation chamber, leaves the accumulation chamber again after a maximum of 10 seconds, preferably after a maximum of 5 seconds. Namely, these mixture components flow substantially at the belt speed through the accumulation chamber. In addition, since there is no procedural need for a static upstream pressure above 5000 Pascal, this value of 5000 Pascal for the static pressure at the bottom of the accumulation chamber is the upper limit for an advantageous embodiment of the method. 5000 Pascal correspond under the above conditions one Liquid column of about 50 cm. The reaction mixture can in principle be discharged from the mixer directly through the feed opening into the accumulation chamber. However, the reaction mixture can also in principle in a preferred embodiment, both on the separation web, which are the same time in the production direction rear boundary of the accumulation chamber as on the separation sheet, which forms the front in the direction of production limitation of the accumulation chamber, or on both separation paths. Therefore, the preferred ranges of the angles of inclination of the respective separating webs in the region of the accumulation chamber are arranged symmetrically to the vertical.

The angle of inclination α of the rear separating web, which forms the rear boundary surface of the accumulation chamber in the production direction, with respect to the horizontal, should preferably be in a range between 10 ° and 170 °, more preferably between 20 ° and 160 ° and most preferably between 45 ° and 135 °.

Likewise, the angle of inclination β of the front separating web, that is to say the front boundary surface of the accumulating chamber seen in the direction of production, should preferably be in a range between 10 ° and 170 °, particularly preferably between 20 ° and 160 ° and very particularly preferably between 45 ° and 135 °.

The gap through which the polyurethane reaction mixture flows out of the accumulation chamber can, in the simplest case, be formed by the narrowest cross-section between the upper separation web, which is pulled over a simple deflection roller, and the lower separation web.

Preferably, however, the gap has a horizontal extent in the flow direction of 5 to 100 cm and particularly preferably of 10 to 50 cm and is formed substantially horizontally. Ideally, the reaction mixture then flows into the subsequent expansion zone with practically no relative velocity to the upper and lower separating web.

The gap can be designed as a shallow channel or as a gap with a progressively widening cross-section, so that the higher velocities of the reaction mixture are reduced when flowing out of the vertically inclined accumulation chamber without flow separation. In this preferred embodiment of the method according to the invention, this gap serves as a buffer and settling zone between the accumulation chamber and the expansion zone. The gap height h is preferably adjustable and is advantageously adjusted so that the gap height h depending on the foaming width b, the

Belt speed v and the volume flow V according to the formula A = * - b - v

wherein the factor k is preferably in a range between 0.8 and 1.2 and more preferably between 0.9 and 1.1 and wherein k can be easily determined experimentally by a person skilled in the art. Foaming width is again understood to mean the width of the polyurethane reaction mixture which foams up on the conveyor belt or base paper, which ultimately corresponds to the width of the resulting foam. This width is determined by the propriety of the side mold walls in the area of the foaming and curing zone. Typically, the foaming widths range between 1, 5 and 2.5 meters.

In this case, the reaction mixture must leave the accumulation chamber essentially liquid, since otherwise it would tend to flow upwards counter to the conveying direction due to the then decreasing density in the accumulation chamber. The gap helps that the reaction mixture over the entire width as possible with uniform speed and as possible without relative velocity to the separation paths, flows into the expansion zone.

Thus, the polyurethane reaction mixture is substantially liquid until it exits the accumulation chamber, i. the reaction mixture is expanded by less than 10%, preferably less than 5%, from the initial state until this time.

In this case, the polyurethane reaction mixture is enclosed during the flow through in the system comprising the accumulation chamber, the gap and the expansion chamber, which is opened only through the feed opening and the outlet opening to the environment. This means that even at the junctions between the accumulation chamber, gap and expansion chamber no PUR reaction mixture can escape.

In a preferred embodiment of the method according to the invention, the gap extends substantially over the entire width of the conveyor belt. Also preferably, the width of the expansion chamber extends substantially over the entire width of the conveyor belt.

The term conveyor belt also includes, for example, an optionally present separating web, such as a base paper, which is guided over the conveyor belt. The terms conveyor belt and separator are therefore used as equivalent terms.

In a preferred embodiment of the method, the gap opening at the output of the

Accumulation chamber designed as a narrow calibration gap. With the help of this preferably adjustable gap, the static height and thus the static pressure can be influenced. In particular, can be influence on the ratio of the static pressure in the middle to the static pressure on the sides, which in turn has a direct influence on the quantity distribution over the width. The more the gap is oriented in the direction of gravitational acceleration, the tighter it can be chosen and the better its distribution effect. The gap width of this calibration gap should preferably be between 0.5 and 30 mm, and particularly preferably between 1 and 20 mm. In this case, the gap width is preferably in dependence on the foaming width b, the viscosity η, the inclination angle δ of the conveyor belt (separating web) in the region of the gap in

Production direction with respect to the horizontal and the volume flow V of the reaction mixture so closely chosen that the gap causes additional damming of the mixture. The gap width s should therefore be preferred according to the inequality

where g is the gravitational acceleration and p is the density of the reaction mixture. The viscosities of the polyurethane reaction mixtures used are generally in a range of 100 to 1000 mPas. The viscosity can be determined, for example, by means of rotational viscometers according to DIN-EN-ISO-3219 at a shear rate of 100 s ^-1 . However, in the determination of the viscosity of polyurethane reaction mixtures, the addition of water and activators and optionally also stabilizers must be dispensed with. Therefore, the measurements have to be carried out without the ingredients of the recipe: catalysts, water and stabilizers, but as these are usually less than 5% by weight of the total amount, the measurements can be so sluggish As the reaction mixture furthermore flows through the gap in a substantially liquid manner according to the invention, the increase in viscosity associated with the progress of the reaction is neglected as well.

The system behaves in principle like hydraulically communicating tubes. In this case, a steady state equilibrium of forces arises between the static pressure of the liquid reaction mixture on the inflow side and the static pressure of the expanding foam in the expansion zone, but additionally the frictional forces of the separation web on the mixture and the momentum forces of the flow act. Due to the large density differences of the liquid reaction mixture compared to the expanded foam a height of a few cm on the inflow side (in the accumulation chamber) is sufficient to compensate for the static pressure in the expansion zone. The foam height, ie the height of the expanded foam is usually in a range between 0.7 m to 1.5 m. Without a tight chambering of this area (ie the accumulation chamber) but would cause the static pressure from the accumulation chamber that the substantially liquid reaction mixture on the inflow side extends over a large area and so a large lake of reaction mixture with a too large average residence time.

The accumulation chamber thus makes it possible, in conjunction with the gap, to produce the necessary pre-pressure over the entire width of the gap, without getting problems from a too large and non-uniform residence time.

The decisive advantage of the invention over the prior art method is the fact that, due to the additional static height in the accumulation chamber before entering the essentially horizontal calibration gap, the driving forces for a relative flow with respect to the separation path above the succeeding To homogenize the width.

The invention also relates to a device for producing polyurethane block foam comprising reservoir for the reactive components polyol and isocyanate, pumps and lines for the metering of the reactive components from the reservoirs to a mixer (1) containing an outflow opening (15) for the free-flowing discharge of Polyurethane reaction mixture, as well as a conveyor belt (7) on which the polyurethane reaction mixture can foam and harden, characterized in that

a) below the at least one outflow opening (15) a stagnation chamber (4) is arranged, which is extended in the vertical direction and closed to the sides, and a feed opening (3) for the supply of polyurethane reaction mixture and in the region of the bottom has a gap opening (5) for the exit of polyurethane reaction mixture, and

b) the accumulation chamber (4) through the gap opening (5) opens into a gap (6), wherein the

Bottom of the gap is formed by a conveyor belt (7) and wherein the gap is closed at the top and bottom and at the lateral edges, and

c) the gap in the expansion chamber (8) opens, wherein the conveyor belt (7) forms the bottom of the expansion chamber (8), and wherein the expansion chamber (8) is closed at the lateral edges, and wherein the flow cross-section of the expansion chamber (8 ) extended in the transport direction of the conveyor belt (7), and d) the expansion chamber (8) has an outlet opening, the system consisting of accumulation chamber (4), gap (6) and expansion chamber (8) with the exception of the feed opening (3) in the accumulation chamber (4) and the outlet opening from the expansion chamber ( 8) is closed on all sides.

The mixer contains an outflow opening for the free-flowing discharge of the polyurethane reaction mixture from the mixer. This means that the outlet opening from the mixer with respect to the feed opening into the accumulation chamber is preferably arranged so that the polyurethane reaction mixture can flow freely out of the outlet opening into the feed opening, wherein between outflow and accumulation chamber quite other components, such as a against the Horizontal inclined task conveyor belt or inclined against the horizontal task plate, can be arranged. The flow path of the polyurethane reaction mixture between the outlet opening and the feed opening is not a closed system, so that gases can escape from the polyurethane reaction mixture. The outflow opening can have any shape, the shape of the gap opening, the round or the elliptical opening are preferred.

In one possible embodiment of the device according to the invention, between the actual mixing element and the outflow opening there is still a hose or a pipeline and optionally also a pressure adjusting device, such as e.g. a choke, arranged.

Preferably, the expansion chamber (8) extends substantially beyond the foaming width b, i. their width is preferably at least 90% of the distance of the lateral mold walls in the foaming and curing zone.

The volume of the accumulation chamber is preferably chosen as a function of the volume flow V such that the residence time t of the polyurethane reaction mixture in the accumulation chamber is a maximum of 10 seconds, preferably a maximum of 5 seconds. Accordingly, the volume of the accumulation chamber is preferred according to the inequality

V ≤ V - t, max

The value for t _max is 10 seconds and preferably 5 seconds. Depending on the belt speeds, the volume flows can be between 30 and 500 kg / min. Preferably, the volume flows are between 50 and 250 kg / min.

The invention is explained in more detail below with reference to the following figures. Show it

1 shows a three-dimensional view of the method according to the invention and the device according to the invention.

Figure 2 is a two-dimensional view of the method according to the invention.

FIG. 1 shows a possible embodiment of the method according to the invention.

The metering units, the tanks and other elements for the processing of the reactive components and the various additional components are not shown in Figure 1.

The tightness of the system in the region of the accumulation chamber 4, the gap 6 and the expansion chamber 8 with respect to the atmosphere by means of e.g. made of sheets produced guide cage 10. The polyurethane reaction mixture is discharged from the mixer 1 through the at least one outlet opening 15 onto a moving task separation web 2 and then flows freely flowing through the upper feed opening 3 into the conically downwardly sloping accumulation chamber 4. The flow space of the accumulation chamber 4 is through the upper feed opening 3, the side walls of the guide cage 10 and the guided along the rear wall of the guide cage task separation path 2, the guided along the front wall of the guide cage rear or upper separation web 12 and by a lower gap opening 5. Subsequently, the reaction mixture is deflected and flows through the horizontal gap 6 before flowing into the expansion zone 8. The expansion chamber 8 is inserted through the side walls of the guide cage 10 and up through the guided along the front wall of the guide cage upper or cover racetrack 12, and down through a rear-fed separating sheet 7, which is folded up on the sides to behind the guide cage a To ensure tight transition to the side sheet 9. The production direction is indicated by arrow 14.

At the same time the task separation sheet 2, on which the mixture was initially discharged, discharged to the rear. The supplied from the rear separator sheet 7 allows the seal against the drive belt 13. After the partially expanded foam strand the

Leaves guide cage 10, the side paper 9 takes over the lateral seal. These

Embodiment with a guide cage 10 represents a relatively simple variant of the method in order to be able to reach the atmosphere in this area from the accumulation chamber 4 to the expansion zone 8. On the inflow side, it is now possible to build up so much static admission pressure that the reaction mixture is conveyed into the expansion zone 8 without appreciable relative flow with respect to the separation path 7. As long as the reaction mixture is fluid, the foam block must be supported even after leaving the guide cage 10 depending on the steepness of the riser even further back to prevent backflow of material in the upper area. For this purpose, mats can be placed on the cover paper with a slight, adjustable force in this area.

Of course, it is also conceivable to dispense with the guide cage 10 and to replace the separating webs instead, e.g. to lead over pulleys or rollers. The lateral seal could also be taken in the area of the accumulation chamber of the supplied from the rear separating web 7, if this is folded up high enough.

It is advantageous, in particular, to guide the separating paths so flexibly that the contour of the flow space in the area from the accumulation chamber 4 to the expansion zone 8 can be varied in a variety of ways. It is important, however, that the separation paths are sealed in the region of the accumulation chamber 4 to the expansion zone 8 at the transitions in a suitable manner.

The most important process parameters are shown in FIG. 2, which shows a possible embodiment of the method according to the invention in a two-dimensional representation.

The reaction mixture is flowed freely from the mixer 1 through the outlet opening 15 directly to the separator sheet 7 and then flows as a film through the feed opening 3 from above into a vertically inclined accumulation chamber 4. This is conical in this case, with the rear or upper Separator sheet 12 in this case has an inclination angle α = 80 ° relative to the vertical, while the separation sheet 7 after deflection in the region of the accumulation chamber 4 has an inclination angle ß = 90 ° relative to the horizontal. The conical accumulation chamber 4 opens into a short, vertically aligned calibration gap with the gap opening 5. The narrower this calibration gap is set, ie the smaller the dimension s shown in FIG. 2 is selected, the higher the mixture accumulates in the accumulation chamber 4 and the better the distribution effect of the calibration gap. Behind the vertically aligned calibration gap with the gap opening 5, the mixture is deflected and flows into the horizontally extending gap 6 of length 1 and the height h. The height h is preferably adjusted so that the mixture can flow through this gap as possible without relative speed to the upper separating web 12 and to the separating web 7. At the outlet cross section of this gap, the reaction mixture then flows into the expansion chamber 8. The production direction is indicated by arrow 14. Due to the static form, it is now even possible in principle, the drive belt (not shown in Figure 2) and thus also adjust the lower separator sheet 7 in the production direction 14 upwards inclined, since a material reflux is reliably avoided. As a result, any precursors of liquid mixture in the bottom region can be reliably avoided, since then the more liquid mixture components would rather flow counter to the production direction relative to the already partially expanded mixture components. This means that the foam tends to "sort" properly in terms of age distribution due to the influence of gravity, as the younger, more fluid mixture tends to be slower than the older, already partially expanded mixture.

In contrast, so far had to be driven in this area usually with a downwardly inclined conveyor belt, as it otherwise on the inflow side to a back flow of

Mixture proportions would come. The consequence of the downwardly inclined conveyor belt in this area is, however, as already explained above, the risk of underflow of already partially expanded, older mixture shares by still liquid, younger mixture shares, since the still liquid mixture proportions in a production direction downwardly inclined conveyor belt due the higher density have a stronger driving force for a flow in the direction of production than already partially expanded mixture proportions.

In a preferred advantageous embodiment of the method, the base paper is therefore in the range of the gap 6 in the direction of production by 0.1 ° to 5 °, more preferably by 0.2 ° to 4 ° and most preferably by 0.5 to 2 ° relative to the Horizontal inclined upwards.

The lower conveyor belt 7 can then either continue to run at a constant inclination angle in the further course or else continue to run over an adjustable fall plate track with variable inclination angles. The advantage of the fall-plate track, which usually consists of four to six adjustable in angle tread plates, is seen in a slightly better density distribution, as the mixture can expand matched to the rising profile of the polyurethane foam down so that the frictional forces of the side paper 9 on the foam counteract the increase in the pressure gradient due to the higher static pressure below and do not act in the same direction as in the case of upwardly expanding foam. For this reason, in a fall plate track to achieve a good rectangular effect usually the mats are placed in the area of the expansion zone 8 with less force than in a system with a constant inclination angle of the lower conveyor belt 7. It is also in the setting Of course, the fall plates should again make sure that the angle of inclination should not be set too steeply depending on the progress of the reaction, since otherwise an underflow of older mixture may occur due to a younger mixture. However, the farther the reaction has progressed, the less likely it is to be undermined. In a particularly advantageous embodiment of the method, which is shown in Figure 2, the foam comes after the free-flowing discharge in atmospheric environment only with moving webs and possibly seals in the corner areas in contact. The PUR reaction mixture is applied directly to the separating web 7 and the separating web 7 is then deflected several times, so that it serves as a boundary surface of the accumulating chamber 4 and the gap 6. A separate task separator is not required in this embodiment. However, the separating web 7 is then preferably guided along under tensile stress on the inside of a bend or a rounding. This is possible, for example, if the bottom paper is guided or held down on the outside in such a way that it also follows this bend or inner radius. Additionally or alternatively, the separating web 7 can be held on the contour by means of vacuum, which should follow it. So that the outer guide or the hold-down does not come into contact with the reaction mixture, the side paper (side paper not shown in FIG. 2, but corresponds to the side paper 9 in FIG. 1) must be supplied from the side in the area of the accumulation chamber and for the lateral sealing in FIG take care of this area.

Possibly. Then, between the laterally fed, and first inwardly running side paper and the separation chamber 7 passing vertically downwards through the accumulation chamber 4, a low-friction sealing material, such as e.g. Teflon board material may be appropriate so that the two separating webs with different conveying directions (separating web 7 down and page paper inside) can easily slip past each other. Behind the kink, the separator sheet 7 can then be folded in the form of a U-fold. In this way, the region of the accumulation chamber 4 and the gap 6 is sealed to the rear or below by the separating web 7. To the sides of the area of the accumulation chamber 4 and the gap 6 by the in the area of the vertically aligned accumulation chamber 4 laterally incoming side papers (side papers not shown in Figure 2, but corresponds to the page paper 9 in Figure 1) and upwards or forwards through the sealed from above into the accumulation chamber rear or upper separator sheet 12 sealed. In the area of the transitions from separating web 7 to page paper 9 or from rear or upper separating web 12 to side paper 9, lip seals may have to be provided which ensure adequate sealing against the reaction mixture at the prevailing static pressure.

Another way to guide the separator sheet 7 so that it follows the bend or rounding would be a deflection over, for example, three rollers (as shown in Figure 2), in which case between the first and the third roller a suitable seal must be present (possibly also a scraper, which strips off the base paper on the first roller), so that the second roller, which would be connected without proper sealing with the flow space, in front of the reaction mixture is protected. Advantageously, the second roller, which comes into contact with the potentially wetted separation web, has a suitable feed to which the reaction mixture is poorly adherent.

Another alternative for guiding the separator sheet 7 in this area exploits the fact that two-layer paper is usually used in which a thin film is applied to a kraft paper. In this case, the kraft paper can be pulled outward around a bent angle profile, while the film runs along the inside and thereby separates the profile from the polyurethane reaction mixture. This embodiment would have the great advantage that in fact no components except the separator sheets come into contact with the reaction mixture. Of course, one could also operate the arrangement shown in Figure 2 so that only the kraft paper, but not in contact with the polyurethane reaction mixture in contact thin film is guided around the rear roller and the film instead continues directly forward. In this case, the film would be separated from the kraft paper in the area of the first of the three rolls and placed back onto it in the area of the third roll.

In a further advantageous embodiment of the method, the rear or upper separating web 12 is pulled at a higher speed compared to the separating web 7 and the side paper. In this way, the effect can be compensated that the speed component of the cover paper in the production direction in the rise zone by the factor cos σ is smaller than the speed at which the cover paper is pulled.

The process according to the invention can be used particularly advantageously for low belt speeds in a range of 0.5 to 3 m / min, preferably 0.8 to 3 m / min and particularly preferably 1 to 3 m / min.

Claims

claims 1. A process for the continuous production of polyurethane block foam, in which the reactive components polyol and isocyanate are metered to a mixer (1) and mixed therein to form a polyurethane reaction mixture and the polyurethane reaction mixture is applied to a conveyor belt (7), foams and hardens on, characterized in that a) the polyurethane reaction mixture after mixing from the mixer (1) through at least one outflow opening (15) is discharged freely flowing and through the feed opening (3) in a stagnation chamber (4) into it, which extends in the vertical direction and after the Pages closed, and in the Area of the bottom in a gap opening (5) opens, and b) the polyurethane reaction mixture in the accumulation chamber (4) is dammed so that static pressure is generated at the bottom of the accumulation chamber over the entire width, and the polyurethane reaction mixture flows through the accumulation chamber (4) from top to bottom, and c) the polyurethane reaction mixture then flows through the gap opening (5) from the accumulation chamber (4) and flows through a gap (6), wherein the underside of the gap is formed by a conveyor belt (7) and wherein the gap up and down and closed at the lateral edges, and d) the polyurethane reaction mixture then from the gap (6) in the Expansion chamber (8) flows into and foams therein, wherein the conveyor belt (7) forms the bottom of the expansion chamber (8), and wherein the expansion chamber (8) is closed at the lateral edges, and wherein the flow cross-section of the expansion chamber in the transport direction of the conveyor belt (7) expanded, and e) the foamed polyurethane reaction mixture emerges from the expansion chamber through an exit opening and optionally further foams and hardens on the conveyor belt (7). 2. The method according to claim 1, characterized in that the reaction mixture from the mixer to a moving task-transport path (2) is discharged and then in the region of the accumulation chamber (4), the gap (6) and the expansion chamber (8) from above, below and the sides between moving transport paths (7, 9, 12) is guided. 3. The method according to claim 1 or 2, characterized in that at the bottom of the accumulation chamber (4), a static pressure between 100 and 5000 Pascal prevails. 4. The method according to any one of claims 1 to 3, characterized in that the polyurethane reaction mixture leaves the accumulation chamber (4) substantially liquid. 5. The method according to claim 1 to 4, characterized in that the gap (6) is expanded in the horizontal direction and extends substantially horizontally. 6. The method according to claim 5, characterized in that the length of the gap (6) in the flow direction in a range between 5 and 100 cm. 7. The method according to claim 6, characterized in that the conveyor belt (7) in the region of the gap (6) relative to the horizontal in the direction of production by an inclination angle δ is inclined upwards. 8. The method according to claim 7, characterized in that the inclination angle δ is 0.1 ° to 5 °. 9. The method according to claim 1 to 8, characterized in that the gap height h as a function of the foaming width b, the belt speed v of Conveyor belt (7) and the mixer (1) leaving the volume flow V according to the formula h = k - ^V b - V is set, wherein the factor k is in a range between 0.75 and 1.25. 10. The method according to any one of claims 1 to 9, characterized in that the accumulation chamber (4) is configured conically in the inlet region. 11. The method according to any one of claims 1 to 10, characterized in that the conveyor belt (7) in the region of the gap (6) relative to the horizontal in Production direction is inclined by an inclination angle δ of at least 10 °, wherein the gap width s of the gap (6) according to the inequality

is selected, and wherein b is the width and δ the angle of inclination of the gap (6), g the Acceleration of gravity, η the viscosity, V the volume flow and p denote the density of the liquid polyurethane reaction mixture. 12. The method according to any one of claims 1 to 11, characterized in that the average residence time of the reaction mixture from the outlet from the mixer (1) until leaving the accumulation chamber (4) through the gap opening (5) a maximum of 15 seconds, preferably a maximum of 10 seconds and more preferably at most 5 seconds. 13. The method according to claim 1, characterized in that the reaction mixture from the mixer (1) directly on the conveyor belt (7) is discharged and the conveyor belt (7) is then deflected several times. 14. Apparatus for producing polyurethane block foam comprising reservoir for the reactive components polyol and isocyanate, pumps and lines for the metering of the reactive components from the reservoirs to a mixer (1) containing an outflow opening (15) for the free-flowing discharge of the polyurethane Reaction mixture, as well as a conveyor belt (7) on which the polyurethane reaction mixture can foam and harden, characterized in that a) below the at least one outflow opening (15) a stagnation chamber (4) is arranged, which is extended in the vertical direction and closed towards the sides, and which has a feed opening (3) for the supply of polyurethane Reaction mixture and in the region of the bottom has a gap opening (5) for the exit of polyurethane reaction mixture, and b) the accumulation chamber (4) through the gap opening (5) opens into a gap (6), wherein the underside of the gap is formed by a conveyor belt (7) and wherein the gap is closed up and down and at the lateral edges, and c) the gap in the expansion chamber (8) opens, wherein the conveyor belt (7) forms the bottom of the expansion chamber (8), and wherein the expansion chamber (8) is closed at the lateral edges, and wherein the flow cross-section of the expansion chamber (8 ) extended in the transport direction of the conveyor belt (7), and d) the expansion chamber (8) has an outlet opening, the system consisting of accumulation chamber (4), gap (6) and expansion chamber (8) with the exception of the feed opening (3) in the accumulation chamber (4) and the outlet opening from the expansion chamber ( 8) is closed on all sides. 15. The apparatus according to claim 14, characterized in that the accumulation chamber (4) in the flow direction has a length of between 1 cm and 50 cm. 16. The apparatus according to claim 14 or 15, characterized in that the volume of the accumulation chamber (4) according to the inequality V <V - T is designed, wherein the average residence time T _v , _ma χ 5 seconds and wherein V is the Volume flow of the liquid polyurethane reaction mixture means. 17. Device according to one of claims 14 to 16, characterized in that the gap (6) is expanded in the horizontal direction and extends substantially horizontally. 18. The device according to claim 17, characterized in that the length of the gap (6) in the flow direction in a range of between 5 and 100 cm. 19. The apparatus of claim 17 or 18, characterized in that the conveyor belt (7) in the region of the gap (6) is inclined in the direction of production relative to the horizontal by an inclination angle δ upwards. 20. The apparatus according to claim 19, characterized in that the inclination angle δ is 0.1 ° to 5 °. 21. Device according to one of claims 14 to 20, characterized in that the gap height h of the gap (6) in dependence on the foaming width b, the belt speed v of the conveyor belt (7) and the mixer (1) leaving the volume flow V of the reaction mixture according to the formula b - v is set, wherein the factor k is preferably in a range between 0.8 and 1.2. 22. Device according to one of claims 14 to 21, characterized in that the accumulation chamber (4) is designed conically in the inlet region. 23. Device according to one of claims 14 to 22, characterized in that the conveyor belt (7) in the region of the gap (6) relative to the horizontal in the direction of production by an inclination angle δ of at least 10 ° inclined, wherein the gap width s of the gap (6 ) according to the inequality

and wherein b is the width and δ the angle of inclination of the gap (6), g the gravitational acceleration, η the viscosity, V the volume flow and p the density of the liquid Polyurethane reaction mixture mean. 24. Device according to one of claims 14 to 23, characterized in that below the outlet opening (15) the conveyor belt (7) is arranged so that the reaction mixture from the mixer (1) can be discharged directly onto the conveyor belt (7), and the conveyor belt (7) is then deflected several times.